Easiest free-software method for simple fiddling with animated gifs that I’ve found is GIMP. Open an animation in there and it puts each frame on a new layer, resize image will scale every layer the same, save (making sure to select “save as animation” when it asks you how to export multiple frames to a gif) and you’re done.

If you were working from scratch, you’d have to put a time in milliseconds in brackets in each layer name – e.g. (100ms), but it’ll put that in for you when you open an existing animation, or you can let it bumume a default value for any unspecified frame when you save it. Also has some handy stuff under Filters>Animation, to optimise files for animation by stripping out the parts of each layer that are on the previous frame and don’t need to be repeated, or to preview the animation in motion. The optimisation can be a bit **** – I’ve had it increase the file size before, but generally speaking it’s an easy tool to use.